Oil burner safety control system



I 177' F as r S 5 2% 5 6 $5 4 Dec. 4, 1956 P. SCHELL 7 2,772,727

OIL BURNER SAFETY CONTROL SYSTEM Filed Jan. 4, 1954 A 24 26 m 22 L76 p I /Z2, I .HHHHH I F 7 66 l I Q l 36 I /Z/ 70 v 75 OPf/VS r AFTER 1 44 r5 a055 66 l, {a

64 7.2 T mg 80 7a! 3a INVENTOR. BY i azzl Jc/ze/l United States Patent OIL BURNER SAFETY CONTROL SYSTEM Paul Schell, St. Joseph, Mich., assignor to Penn Controls, Inc., Goshen, Ind., a corporation of Indiana Application January 4, 1954, Serial No. 401,745

1 Claim. (Cl. 158-28) This invention relates to an oil burner control which, in addition to handling the regular functions of the usual oil burner control, including an initial combustion failure shut-down and delayed ignition tripping, has the feature of low voltage protection without the necessity of balancing impedances, and protection for combustion failure subsequent to successful establishment thereof which results in recycling if the burner will then operate properly, or shuts the burner down if it fails to do so.

One object of the invention is to provide a main relay and a combustion thermostat for controlling the burner blower motor and the ignition of an oil burner or the like in such manner that the features above mentioned can be obtained with complete safety of operation, a negative temperature coetficient resistor being provided in the circuit to delay pull-in of a secondary relay which, when it becomes operative, accomplishes the ignition tripping operation.

Another object is to provide for low voltage protection by reducing the current flow in the main relay immediately after it is energized so that it will drop out upon predetermined drop in line voltage. In explanation of this feature, I provide a main relay which is operable to cut in at as low as 85% of the full line voltage and to cut out at a point not lower than approximately 70% thereof in contrast with the usual arrangement wherein relays are used for burner control circuits and the relay when properly designed to give sufficient motion for operation of the contacts cuts out at about 35% of the full line voltage. Provision for low voltage protection is particularly important because at about 65% of the full line voltage the burner functions improperly, its efficiency is low, the air velocity is subnormal, oil pressure (in some types of burners) is also subnormal and the flow through a solenoid valve provided to control the oil supply is restricted. Also low voltage in the ignition transformer causes either entire loss of spark or irregular occurrence thereof which results in the burner popping and sometimes in an explosion. The problem is worse in small communities where consumption varies greatly and in almost all localities when sleet gathers on the transmission wires and causes a temporary drop in voltage which may last sometimes for an hour or more. In view of the foregoing problems, cut-out of the relay at or above 70% of the full line voltage is desirable.

Another object of the present invention is to provide a circuit arrangement for a relay to make it possible for it to cut in at one voltage and thereafter remain in cut-in position on reduced voltage thus making it easier to drop out subsequently when the voltage in the line lowers, the relay drop-out occurring preferably before an excessive lowering; whereas maintenance of the initial full line voltage results in the necessity of requiring an excessively low voltage before drop-out will occur.

Still another object is to provide a main relay for closing the blower motor and ignition circuits when a room thermostat calls for heat, the ignition circuit being also controlled by a switch which is opened by energization of a second relay coil, the circuit of which includes a negative temperature co-elficient resistor to give delayed action.

A further object is to provide the circuit with a safety switch for effecting normal shut-down following initial combustion failure, and following subsequent combustion failure if a recycling of the control does not occur, the safety switch requiring manual resetting so that the trouble that caused shut-down must be remedied before such manual resetting operation can be effective for placing the control back in automatic operation.

Still a further object is to provide a switching arrangement electrically connected with the main relay so as to cooperate therewith in providing an initial circuit of given voltage for the relay and a subsequent lower voltage circuit to accomplish the low voltage protection feature hereinbefore referred to.

An additional object is to provide a circuit arrangement that affords low voltage protection by the relay pulling in from the entire secondary of a transformer and thereafter remaining energized from a portion only thereof so that when the relay pulls in under poor voltage conditions, a subsequent small drop in voltage will effect dropout of the relay Another additional object is to provide a control circuit arrangement wherein the current for the room thermostat is substantially constant during initiation and running of the burner and during all steps in the cycling thereof, a transfer switch being provided for transferring the current through the relay from one portion of a circuit to another, and the resistance in the various circuits being substantially the same so as to eliminate a critical requirement with respect to balancing the impedances of various components of the circuit.

With these and other objects in view, my present invention consists in the construction, arrangement and combination of the various parts of my oil burner control, whereby the objects contemplated are attained, as hereinafter more fully set forth, pointed out in my claim and illustrated in the accompanying drawings, wherein the figure is an electro-diagrammatic view of an oil burner control embodying my present invention.

On the accompanying drawing I have used the reference character M to indicate the blower motor of a burner B which is shown diagrammatically and is of the usual type used in oil heated furnaces. The blower of the motor is shown at 21. For igniting the combustible mixture of atomized fuel oil and air, ignition mechanism is provided which is shown diagrammatically at Ign.

A transformer T is shown having a primary P and a pair of low voltage secondary coils S and S for instance, 12 volts each, the primary being for the usual house current of or 230 volts. Line wires 10 and 12 for supplying current to the primary P are shown and these also supply current for the motor M by means of a wire 14 which leads from the line wire to a main switch MS and wires 16 and 18 which lead from the main switch to the motor M and another wire 20 connecting the motor to the line wire 12.

The ignition Ign is in parallel with the motor M through wires 22, 24 and 26, an ignition switch IS being in circuit therewith so that the current from 10 through 14, MS, 16 and 22, and through 24, Ign and 26 is controlled thereby.

The low voltage circuits supplied by the secondary coils S and S of the transformer T include wires 28 and 30, and a wire 32 from a center tap of the secondary so that any circuit across 28 and 30 is energized from the entire secondary of S plus S and individual circuits may be energized across wires 28 and 32 for the secondary coilsS and across wires 30 and 32 for the secondar coil S the right-hand end of S The wire 32 is connected by wires 34 and 36 to normally closed contacts of a safety switch SS. The initial room thermostat circuit includes these contacts, a normally open room thermostat RT, a main relay coil RC a normally closed first transfer switch TS, a normally closed first combustion switch CS and a safety switch actuator SSA in the form of a heater for a bimetal element 38. The elements just enumerated are connected with the safety switch SS and between the wires 28 and 30 by a series of wires 42, 44, 46, 36, 37, 54 and 40. The wire 32 extends to normally open contacts of a holding switch HS, the other side of which is connected by a wire 34 to the junction of the wire 37 with the switch TS A second relay coil RC is connected from wire 28 to wire 32 by means of wires 53, 5?, 6t 52, 56, 37 and 34, with a negative temperature coefficient resistor NTCR interposed between the wires 58 and 59 and a normally open combustion switch CS interposed between the wires 52 and 56.

The circuit arrangement includes further two other wires 48 and 50 connected with the junction between wire 36 and the safety switch SS, and the junction between wires 60 and 52, a second transfer switch TS (normally open) being interposed between wires 48 and 50.

The second relay coil RC which, as indicated by the arrows 64, 66 and 68, opens the ignition switch IS, also closes the transfer switch T8 and opens the transfer switch TS. The relay coil RC when energized, closes the main switch MS, the action being indicated by the arrow 76 and closes the holding switch HS (arrow 70).

The bimetal element 38 when heated for about 90 seconds by the safety switch actuator SSA opens the safety switch SS as indicated by the arrow 72 and the safety switch is latched in the open position by a latch 74 pivoted at 78, which latch may be manually released for reset by pressure on one end thereof as indicated by the arrow 80.

The combustion switches CS and CS are actuated by a bimetal element 82 which warps upwardly under the action of the heat of combustion in the furnace. This element carries a friction surface 84 with which a friction shoe 86 is engaged by a spring S8 to open the switch CS and close the switch CS as indicated by the arrows 90 and 92. The friction connection insures immediate operation of the combustion switches upon either a rise or a drop in furnace temperature. The switches TS and TS have overlapping contacts and therefore operate in a sequence as indicated by the legend on the drawing TS Opens After TS Closes. The room thermostat RT, of course, is normally open, closing only when the room calls for heat, the open position being shown which corresponds to the idle position of the control.

PRACTICAL OPERATION Normal starting and rumting.-When the room thermostat RT calls for heat, it energiezs the relay coil RC to close the main switch MS and thereby energize the burner motor M and the ignition Ign, the switch IS being closed at that time. The circuit for RT may be traced from the left end of S through 28, 4-2, RT, 44, RC 46, SS, 36, T5 37, 54, CS 40, SSA and 30 to The relay coil RC is thereby energized by the entire secondary (S plus S of the transformer T with a slight voltage drop occurring through SSA.

As soon as the holding switch HS closes, two circuits are established, one of which is energized from the secondary coil S and the other of which is energized from the secondary coil S The circuit from S is now a room thermostat circuit through the transfer switch TS but instead of through wires 37, 54, 4t) and 30, the circuit is through the wires 34 and 32, and the holding switch HS to the center tap of the transformer secondary. The circuit from S is established from this center tap through 32, HS, 34, 37, 54, CS 40, SSA and 3b to the right-hand end of S each independent of the other.

Combustion establishment acts on the bimetal element 32 to open CS and then close CS Closure of CS is for the purpose of partially establishing a subsequent combustion failure circuit. Closure of CS also energizes RC through NTCR. Opening of CS breaks the circuit of the safety switch actuator SSA so that the safety switch SS will not trip out since combustion has been successfully established. The switches CS and CS are operated usually within 60 seconds; whereas the safety switch actuator SSA will cause the safety switch SS to trip out in about seconds if there is no flame to actuate 82, thus giving the necessary leeway for prevention of undesirable safety switch actuation.

The presence of NTCR in the circuit of RC delays the operation of RC for any desired period of time between a few seconds and. 90 seconds after the circuit is established and thereupon the secondary relay coil RC due to the decrease in resistance of NTCR, operates the switches IS, TS and T5 The delay period just referred to should be for best operation long enough for CS to make contact firmly so as to reduce false recycles due to CS opening momentarily after closing which could hap pen with irregular temperature rise affecting bimetal element 82. The opening of the switch IS, of course, deenergizes the ignition Igu which is no longer needed. The switches TS and TS effect transfer of the circuit of the relay coil RC from through the switch T8 to through the switch T5 the circuit then being from RC through 46, SS, 48, TS 50, 52, CS 56, 37, 34, HS and 32 to the center tap of the transformer secondary.

Normal shut-d0wn.-When RT becomes satisfied, it opens the circuit through RC and thereby MS opens in order to de-energize the motor M and HS opens to deenergize the secondary relay coil RC so that IS, TS and TS revert to the initial or idle position and are thus conditioned for the next cycle of operations. Within a few minutes CS recloses and CS reopens as the bi-metal element 82 cools. All parts are then in position for recycling when the next call for heat occurs at the room thermostat.

Initial combustion failm'e.If the burner fails to start properly, the burner shuts down because of CS failing to open because no heat is being applied to the combustion responsive bimetal element 82 and therefore the safety switch actuator SSA remains energized through the holding switch HS from the secondary coil S in about 90 seconds, therefore, the safety switch actuator so affects the bimetal element 38 as to trip the safety switch SS to the off position. The main relay coil RC is thereby tie-energized for opening the main switch MS, whereupon the trouble must be remedied and the safety switch manually reset by pressure at Sit to swing 74 on its pivot 78 so that its cooling or cooled bimetal element 38 may spring down again to the latched position and thus permit the safety switch contacts SS to close.

Subsequent combustion failure.-This type of failure occurs after combustion has been successfully established and is the result of some fault such as water in the fuel extinguishing the flame. The combustion chamber or stack, as soon as it starts to cool, permits the bimetal element 82 to cool also for reopening the combustion switch CS and then reclosing the combustion switch CS The opening of CS breaks the circuit of the relay coil RC which at that time is through the transfer switch TS so that the main switch MS opens and thus de-energizes the motor M. Thereupon a recycle condition is established by the opening of CS also breaking the circuit of RC and that, of course, results in reclosing of the ignition switch IS, reclosing of the transfer switch TS and reopening of the transfer switch TS The burner then gets a fresh start and will run normally if the trouble that caused subsequent combustion failure has by that time remedied itself. If it hasnt, the

safety switch SS will open in about 90 seconds due to rte-energization of SSA so that remedy of the trouble and resetting of SS are then necessary as explained in connection with initial combustion failure.

The disclosed control circuit has the desirable features of recycle, fixed time delay for the ignition, positive ignition on recycle, and safety lock-out on flame failure or on failure to establish flame on start. In general the recycle feature results in (after the ignition has been turned off) opening of the hot combustion thermostat contacts which indicated flame failure and immediately turns the burner off and keeps it off for a short period of time and then turns it on again in the same manner as a cold start.

The disclosed circuit also has extended ignition time since ignition is not turned off until some delay period of time which is predetermined by NTCR and its effect on RC after the combustion thermostat has indicated establishment of flame. The circuit has the necessary components to give low voltage protection and a relatively constant thermostat current in that subsequent phases of the operation after an initial energization resulting from ciosure of the room thermostat do not change the thermostat current other than to secure the desired voltage for low-voltage protection.

My circuit arrangement provides an oil burner control which does not require balancing of impedanees for the starting and running circuits in order to have the advantage of low voltage protection When running, the control supplies current from S for the relay coil RC with current for the secondary relay coil RC being in parallel with RC. The transfer switches T3 and TS in either position do not throw in or remove any impedances with respect to the main relay coil circuit in its running position as in one instance the current passes through the switch TS to the holding switch HS and in the other instance through the switches T5 and C5 to the holding switch. The coils S and S are of such value as to require the voltage from more than 5 alone and less than S plus 5 to pull the relay in while S alone is sufficient to hold it in and cause it to drop out when the voltage drops about 30%, the coil S at the same time furnishing sufficient current for the NTCR and RC circuit.

Some changes may be made in the construction and arrangement of the parts of my oil burner control without departing from the real spirit and purpose thereof, and it is my intention to cover by my claim such modified forms of structure and use of mechanical equivalents as may reasonably be included within its scope.

I claim as my invention:

An oil burner control mechanism of the type which controls an oil burner and its ignition means in response to actuation of a remote control switch, said mechanism comprising: a main switch, burner motor and ignition circuits controlled thereby; a transformer providing a source of electrical power; a control circuit network connected across the secondary of said transformer, a room thermostat, a holding switch, a safety switch, and a delayed safety switch actuator all connected in said circuit network; an electromagnetic operator connected in said network and adapted upon energization to close said main switch and said holding switch; combustion responsive means including in said network cold contacts closed only in the absence of combustion and hot contacts closed only in the presence of combustion; a transfer switching mechanism including normally open and normally closed contacts in said network and a transfer switch operator therefor; said control circuit network including an initial energizing circuit for said electromagnetic operator comprising said transformer secondary, room thermostat, safety switch, normally closed transfer switch, closed cold combustion contacts and said safety switch actuator; a holding circuit for said electromagnetic operator energized by a segment of said transformer secondary and including the elements of said initial circuit but by-passing said closed cold combustion contacts and said safety switch actuator by means of said holding switch; a maintaining circuit for said electromagnetic operator energized by a segment of said transformer secondary and including said room thermostat, safety switch, normally open transfer switch, closed hot combustion contacts and said holding switch; and means controlling energization of said transfer switch operator and consequently the transfer of the energizing circuit for said electromagnetic operator from said holding circuit to said maintaining circuit, said last mentioned means including a circuit energized by a egment of said transformer secondary and connecting in series said transfer switch operator, the closed hot combustion contacts and a resistor having a substantial nega tive temperature coeflicient of resistance said resistor being adapted to delay energization of said last mentioned circuit for a predetermined time after closure of said closed hot combustion contacts.

References Cited in the file of this patent UNITED STATES PATENTS 1,516,646 Roseby Nov. 25, 1924 2,040,402 Persons May 12, 1936 2,064,181 Rubel Dec. 15, 1936 2,385,426 Taylor et al Sept. 25, 1945 2,592,827 Schell Apr. 15, 1952 2,604,148 Witherspoon July 22, 1952 

